Organisms with longer digestive systems needed to break down difficult to digest food are usually herbivores.
Herbivores primarily consume plant material, which can be tough and fibrous. Plants contain cellulose, a complex carbohydrate that most animals cannot digest efficiently. Therefore, to extract nutrients from their plant-based diet, herbivores have evolved longer and more complex digestive tracts. This extended digestive system allows them more time to break down cellulose and absorb nutrients effectively.
In contrast, carnivores, which primarily eat meat, have shorter digestive systems because meat is easier to digest. Omnivores have a mixed diet and generally have a digestive system that falls somewhere between that of herbivores and carnivores. Detritivores consume decomposing organic matter and have different digestive adaptations suited for breaking down decaying materials.